A centrifugal pump for a fluid converts pump input power to kinetic energy in the fluid by means of a revolving device such as an impeller that accelerates the fluid. The most common type of centrifugal pump is the volute pump. Fluid enters the pump through the eye of the impeller and the impeller rotates at high speed. The impeller accelerates the fluid radially outward toward the pump volute or casing. This acceleration of the fluid creates suction at the impeller's eye that continuously draws more fluid into the pump.
The energy that the pump transfers to the fluid is kinetic energy, and is proportional to the velocity at the edge or vane tip of the impeller. The faster that the impeller revolves or the bigger the impeller is, the higher will be the velocity of the energy transferred to the fluid. The purpose of the pump volute or casing is to recover and convert this kinetic energy back to static pressure that a downstream system may more efficiently use. A pump of the centrifugal type may have an annular diffuser that circumscribes its impeller to help diffuse the high velocity discharge of the fluid at the impeller edge and thereby increase conversion of kinetic energy to static pressure. The annular diffuser accomplishes this diffusion with multiple diffuser passageways that extend at an angle from the impeller edge toward the volute and have an area that expands with distance from the impeller edge.
Installation of such an annular diffuser requires that the pump volute have a large diameter split line to install the annular diffuser. This results in a larger diameter volute with increased bulk and weight. Furthermore, the solid ring annular diffuser requires elaborate sealing and venting elements to eliminate leakage and axial loading.